i was always tols this is a loop or curve radius on a ogauge layout there is different curves to this 72 is the highest so far ive hurd theres going to be bigger stuff idk how true this is. i hope this help you understand how it works. if you do need more info go to MTH,LIONEL or any ogauge department here or other wise it will explain more on how it works,the higher track(72) you go the bigger room you need the lower the sharper curve you get chances of derailment will accure. hope this helps and happy rail to you chad noel from pittburgh pa.
No, it's the diameter. For older, tubular track, it is the (often approximate) diameter of a circle of track to the outer ends of the crossties. For newer track types, it is probably the actual diameter of the circle made by the center rail. O27 is exact to the ends of the ties, with a 12.5-inch radius to the center rail. O31 (originally just "O", sometimes called "O30") is approximate to the ends of the ties (30.534 inches exactly), with a 14.142-inch radius to the center rail.
Bob Nelson
That is the radius measured in inches. An O27 radius would need 27 inches to make a semi-cicle, a O72 radius would need 72 inches to make a semi-cicle. Depending on the manufacture the track may have different rail height even if the radius is the same.
Bill T.
Try the Classic Toy Trains forum. This is for 1:1 scale trains.
what is the difference between 27" 31" 42" 54" 72" tracks
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